The present invention relates to electric motors and, more particularly, to control systems for starter motors used with internal combustion engines.
Lawn mowers, tractors, automobiles, and other power equipment and vehicles often rely on internal combustion engines to supply power to drive various tools such as mower blades, power-take-off units, and the like; to supply power for locomotion; or both. An internal combustion engine may be started using an electric starter motor. The engine may also be coupled to a generator or alternator that produces electric energy. Energy from the alternator is used to recharge a battery that powers the starter motor during starting. The battery also provides power to the electrical system of the power equipment or vehicle and any internal or external devices connected to the electrical system.
While engines with starter motors and electrical systems as described above are functional, they have many shortcomings. Some of these relate to the electric starter. Typical electric starters for internal combustion engines include gearing for driving the engine flywheel. Once the internal combustion engine is started, the electric starter is mechanically disengaged from the flywheel. The gears and the engagement/disengagement mechanism are relatively complex and expensive to manufacture. In addition, these components are subject to wear and, therefore, have a limited operational life. Conventional starters are also noisy, which is an annoyance to people operating them, and have relatively long start times.
Other shortcomings with conventional starting systems relate to the alternators used in the systems. Known alternators usually must be coupled to voltage regulators to provide suitable voltage output. The need to have a voltage regulator adds cost and complexity to a starting system. Typical alternators are also incapable of supplying sufficient current output to meet the requirements of modern electric power demands. Yet another disadvantage of conventional starting systems is that they require a separate starter motor and alternator (or generator). This increases the cost of a starting system.
There have been some attempts to improve starting systems for internal combustion engines. For example, the starting system disclosed in U.S. Pat. No. 4,720,638 (the xe2x80x9c""638 patentxe2x80x9d), commonly assigned with the present application to Briggs and Stratton Corporation, discloses an electronically-commutated, DC starter motor/alternator for an internal combustion engine. The system disclosed in the ""638 patent does not require a separate starter and alternator. Instead, the system uses a stator mounted directly to the engine and a rotor that also acts as a mechanical flywheel. This type of configuration is sometimes referred to as an xe2x80x9cintegral flywheel-rotorxe2x80x9d starter. However, the electronic control system disclosed in the ""638 patent does not provide all of the regulation and control functions that are desirable for modern applications (such as using an internal combustion engine as an electric-power-generation unit for backup and remote supply of electric power). Another deficiency of the system shown in the ""638 patent is that its flywheel is relatively heavy and has a relatively inefficient electromagnetic design.
Accordingly, there is a need for an improved control system for starter motors, including integral flywheel-rotor starters.
The present invention provides a control system for an electric motor used with an internal combustion engine wherein the engine flywheel and the motor""s rotor are integrally-formed. The system preferably includes a starter motor, although it may be used with other types of motors. The motor has a stator mounted co-axially with the engine crankshaft and a rotor positioned radially outward from the stator. A sensor is positioned near the rotor for sensing its rotational speed. The sensor is coupled to a controller. The controller is operable to deliver an output signal to the stator to start the internal combustion engine.
While the starter motor starts the engine, a processor provides a signal resulting in the starter motor xe2x80x9csteppingxe2x80x9d (i.e., incrementing the speed by discrete values) from a low speed to a high speed. Once the engine has started and the engine speed is greater than a predetermined trigger speed, the processor delivers another output signal such that the motor commutates at a speed that is less than the speed of the rotor. This results in a motor slip, and by commutating the motor in this manner the motor acts as a generator. The motor slip is regulated when the motor is generating electric power so that the motor produces a constant output voltage.
Other features and advantages of the invention will become apparent by consideration of the detailed description and accompanying drawings.